(MOdulator-DEModulator) Until the late 1990s, the term stood for a device that allowed a computer or terminal to transmit data over a standard dial-up telephone line. Since the advent of high-speed cable and DSL connections, modem may refer to devices for low-speed dial-up or high-speed broadband.
This definition pertains only to dial-up modems, which convert digital pulses from the computer to audio tones that an analog telephone line is set up to handle and vice versa. V.92 is the last dial-up standard, providing a data rate of 56 Kbps (see V.92). For high-speed broadband modems, see cable modem, DSL and cellular modem.
Like a Telephone
A modem dials the line and answers the call. It performs the digital-to-analog and analog-to-digital conversion while controlling transmission speed. Whatever the top speed, some lower speeds are supported to accommodate old modems or negotiate downward on noisy lines. Over the years, speeds evolved from 300 bps to 56 Kbps.
Built In Today
New computers geared to the home user generally have a built-in modem, while those targeted for the office may not. A modem can be added internally via a PCI card, or externally via a serial or USB port. In Windows, the Dial-up Networking "Make New Connection" wizard takes you through setting up your modem to dial your Internet provider.
Error Correction and Compression
Modems have built-in error correction (V.42) and data compression (V.42bis, MNP 5). On files that are already compressed, the hardware data compression adds little value, because it cannot make compressed files smaller. Modems also have automatic feature negotiation, which adjusts to the other modem's speed and hardware protocols.
The Hayes Standard
Most modems use the Hayes AT command set, which are machine instructions for modem control. The term modem has been used as a verb; for example, "I'll modem you later." See modem status signals and AT command set.
The Sportster
The Sportster was one of the hottest-selling products in the 1990s as people went online in record numbers. External units have the advantage of status lights, which help troubleshoot connections. Internal modems have since become the norm. (Image courtesy of 3Com Corporation.)
A Rack of Hayes Modems
Hayes was the pioneer in personal computer modems and set the standard for control commands. Hayes produced a full line of modems from singles to rack-mounted units such as this model with 16 modem cards. Allowing card replacement with power on, rack-mounted modems like these are found by the thousands at large ISPs. (Image courtesy of Hayes Microcomputer Products, Inc.)
This definition pertains only to dial-up modems, which convert digital pulses from the computer to audio tones that an analog telephone line is set up to handle and vice versa. V.92 is the last dial-up standard, providing a data rate of 56 Kbps (see V.92). For high-speed broadband modems, see cable modem, DSL and cellular modem.
Like a Telephone
A modem dials the line and answers the call. It performs the digital-to-analog and analog-to-digital conversion while controlling transmission speed. Whatever the top speed, some lower speeds are supported to accommodate old modems or negotiate downward on noisy lines. Over the years, speeds evolved from 300 bps to 56 Kbps.
Built In Today
New computers geared to the home user generally have a built-in modem, while those targeted for the office may not. A modem can be added internally via a PCI card, or externally via a serial or USB port. In Windows, the Dial-up Networking "Make New Connection" wizard takes you through setting up your modem to dial your Internet provider.
Error Correction and Compression
Modems have built-in error correction (V.42) and data compression (V.42bis, MNP 5). On files that are already compressed, the hardware data compression adds little value, because it cannot make compressed files smaller. Modems also have automatic feature negotiation, which adjusts to the other modem's speed and hardware protocols.
The Hayes Standard
Most modems use the Hayes AT command set, which are machine instructions for modem control. The term modem has been used as a verb; for example, "I'll modem you later." See modem status signals and AT command set.
The Sportster
The Sportster was one of the hottest-selling products in the 1990s as people went online in record numbers. External units have the advantage of status lights, which help troubleshoot connections. Internal modems have since become the norm. (Image courtesy of 3Com Corporation.)
A Rack of Hayes Modems
Hayes was the pioneer in personal computer modems and set the standard for control commands. Hayes produced a full line of modems from singles to rack-mounted units such as this model with 16 modem cards. Allowing card replacement with power on, rack-mounted modems like these are found by the thousands at large ISPs. (Image courtesy of Hayes Microcomputer Products, Inc.)
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2008 The Computer Language Company Inc. All rights reserved. |
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